Conventionally, this kind of hoist traction machine is well-known and is disclosed in, for example, the Japanese Patent Publication Gazette No. Sho 54-9381. The hoist and traction machine disclosed therein is so constructed that, as shown in FIG. 14, onto a driving shaft B in association with a load sheave A through a gear reduction mechanism is mounted a driven member C non-rotatable relative to the driving shaft B, a driving member D provided at the outer periphery with teeth N is screwed with the driving shaft B, between the driven member C and the driving member D are interposed a braking ratchet wheel F engageable with a braking pawl E and braking plates 6 so as to construct a mechanical brake, and a lever H for driving the driving member D in the normal or reverse direction is provided at the driving member D. The lever H is operated to normally or reversely rotate the driving member D through a change-over pawl I selectively engageable with one of the teeth N, so that the mechanical brake comprising the braking ratchet wheel F, braking plates G, driving member D and driven member C, is operated, thereby enabling a chain J engaging with the load sheave A to hoist, lower or haul a load.
The hoist and traction machine constructed as mentioned above is provided with a free rotation control apparatus to be discussed below, which can quickly pull out the chain J toward the load side thereof in the no load state without operating the mechanical brake so as to elongate the chain at the load side, or can pull the same at the no-load side so as to be quickly reduced in length at the load side.
In detail, the free rotation control apparatus is provided between the driven member C and the driving member D with an elastic resistance member K for applying resistance against the movement of the driving member D toward the driven member C and adapted to produce a small gap Q between a holding member L fixed to the driving member D and a stopper M fixed to one axial end of the driving shaft B, during the rotational braking of the load sheave A. The change-over pawl I is set in the neutral position and the chain in the no-load state is pulled at the load side so that the driving shaft B rotates, but the driving member D is suppressed of from moving toward the driven member C due to resistance of the elastic resistance member K. Hence, the mechanical brake does not operate and the load sheave A is freely rotatable, thereby enabling the load sheave A to be put in the free rotation state and the chain J to be quickly drawn out.
Such a conventional free rotation control apparatus, which applies resistance only by the elastic resistance member K against the movement of driving member D toward the driven member C, so that, when the chain J in the no-load state is drawn in the state of disengaging the pawl I from the teeth N, if the drawing speed is too fast and the drawing force too strong, the driving member D moves toward the driven member C overcoming resistance of the elastic resistance member K and the mechanical brake operates, thereby not enabling the load sheave A to freely rotate, so that an input range of a drawing force is restricted. Accordingly, while the drawing speed, that is, a force to draw the chain J, is being adjusted, the chain J in the no-load state should be drawn without operating the mechanical brake, thereby creating the problem in that it requires skill to freely rotate the load sheave A.